Bloodfall (An Undertale AU)

Ever since the death of his younger brother. Things have gone downhill in the surface world for Sans. Alphys died a few months after Papyrus to a disease, Mettaton and Undyne, especially Undyne, had fallen into a depression. Flowey dissapeared into mt. Ebott, not to be found and Sans is fighting depression and insanity.

One day, Sans discovers a suspect to his brother's death. A being that is trapping anyone who had either fallen into Mt. Ebott or stayed behind in snowdin for a while. Sans, along with Frisk and Undyne, go into the underground themselves to confront this being. They must encounter the Bloodfall that traps and kills anyone who dares pass by waterfall.

(This takes place after a true pacifist run if one killed Sans in a Genocide run, but reset their game before getting to Asgore(I did this in a way to quit the Genocide route). This is if Frisk choses to do this the Pacifist way. I might make a Genocide one in Story Shorts. Also, My Sans is a human, but feel free to interprate him as a Skeleton if you ever choose to use this AU. Just credit me!)